"Naval mines achieved several striking successes during World War II. In the Pacific, naval mines proved more destructive to the Japanese war effort than the atom bombs. During a 10 week period between April and August 1945, 12,000 mines were delivered by American bombers. These destroyed 1,250,000 tons of Japanese shipping (670 ships hit, 431 destroyed). That's 18 mines for each ship hit. The Americans had air superiority, so losses during these 1,500 missions amounted to only 15 planes, most of them to accidents. Had these missions been flown against opposition, losses would have been between 30 and 60 aircraft, plus similar losses to their fighter escorts. But even those losses were, in wartime, a victory if you destroyed or damaged 670 enemy ships.

A conventional submarine campaign was also waged against Japanese shipping. Comparisons to the mine campaign are interesting. A hundred submarines were involved in a campaign that ran for 45 months from December, 1941 to August, 1945. Some 4.8 million tons of enemy shipping was sunk. For every US submarine sailor lost using submarine launched torpedoes, 560 tons of enemy ships were sunk. During the mine campaign, 3,500 tons were sunk for each US fatality. On a cost basis, the difference was equally stark. Counting the cost of lost mine laying aircraft (B- 29's at $500,000 each) or torpedo armed submarine ($5 million each), we find that each ton of sunk shipping cost six dollars when using mines and fifty-five dollars when using submarines. These data was classified as secret until the 1970s. It indicates that mines might have been more effective than torpedoes even if the mines were delivered by submarine."

By the time the US started the aerial mining campaign, the IJN had lost most of its ships and fuel was a critical commodity. Also PB4Y patrols from Okinawa were patrolling the region and any minesweepers ran the risk of being attacked from the air.

A submarine based mine laying operation starting early in the war may have been more successful than using torpedoes, but probably not dramatically so. Japanese mine sweepers probably would have found a significant number of the mines before they had a chance to take out merchant shipping.

The Germans and British mined each other's waters from the start of the war and while there were some mine successes, neither campaign was as dramatically successful as the American mining of Japanese waters because a lot of the mines were detected and swept.

The crews also knew that a single bullet into a bomb bay could spell their doom.

They may have worried about it, but the statistics show that this was far better in saving crews than other combat missions, no? Also, i would guess that the same worry would apply to a bomber loaded with regular 500 pound bombs, or even incendiaries.

Not long after the capture of the Marianas while the B-29 units were getting organized for the bombing campaign, the USAAF sent photo recon B-29s over Japan to film the run into each target. My father was one of the photographers. He said it was somewhat satisfying to watch the Japanese fighters trying to claw their way up to their altitude only to be left behind.

His next assignment was flying B-25s out of Attu on low altitude anti-shipping and attacks on bases in the Kuriles. He liked the B-25, but I think he has PTSD from all the flak. He said his plane was never hit, but he has a shot of a B-25 that took a direct hit over Paramushiro Jima most of it was a sheet of fire.